In an existing 3rd Generation Partnership Project (3GPP) Evolved Universal Terrestrial Radio Access (E-UTRA) system, network side equipment, for example, a base station (BS), delivers downlink control signaling before sending downlink data, so as to instruct a user to receive the downlink data from corresponding resources. Upon receiving the downlink data, the user feeds back an acknowledgement (ACK) if the downlink data is correctly received; otherwise, the user feeds back a negative-acknowledgement (NACK). User equipment (UE) that receives the downlink data may support two modes, namely, a frequency division duplex (FDD) mode and a time division duplex (TDD) mode.
For the UE that supports the TDD mode, channels for carrying the ACK/NACK feedback information of the user are ACK channels. The ACK channels are assigned by the network side according to a rule predefined by the system. The user has already acquired the predefined rule, and detects the assigned ACK channels according to the predefined rule, and then carries the feedback information on the channels and sends the feedback information to the network side equipment.
In the prior art, a frame structure in the TDD mode is generally as shown in FIG. 1. Each radio frame is 10 ms long, and consists of two half-frames that are respectively 5 ms long. Each half-frame consists of eight slots that are respectively 0.5 ms long and three special fields, DwPTS, GP, and UpPTS. Every two slots constitute one sub-frame, and the three special fields, DwPTS, GP, and UpPTS, constitute a special sub-frame. Each sub-frame is 1 ms long. Among the sub-frames, the sub-frames 0 and 5 are downlink sub-frames, the sub-frame 2 is an uplink sub-frame, DwPTS in the special sub-frame may transmit downlink data or may not transmit data, and the remaining sub-frames may be flexibly assigned as uplink sub-frames or downlink sub-frames.
Currently, seven downlink-to-uplink configurations are defined in the 3GPP E-UTRA system, including three configurations for the 5 ms downlink-to-uplink switch-point periodicity, namely, 1:3, 2:2, and 3:1; and four configurations for the 10 ms downlink-to-uplink switch-point periodicity, namely, 6:3, 7:2, 8:1, and 3:5. Except the two ratios of 1:3 and 3:5, all the other ratios are required to feed back ACKs or NACKs of N (N>1, N is an integer) downlink sub-frames in one uplink sub-frame. As known to those skilled in the art that, N>1 is a unique condition for the TDD mode, and the ACK/NACK assignment problem for a plurality of downlink sub-frames under this condition needs to be solved. Meanwhile, the solutions proposed under the condition of N>1 should also cater to the condition of N=1, so as to reduce the complexity of the system in the TDD mode.
As the time-frequency resources occupied by a physical downlink control channel (PDCCH) are measured by taking control channel elements (CCEs) as the unit, an ACK channel for ACK or NACK uplink feedback is implicitly mapped by a CCE with the smallest label occupied by the PDCCH. A commonly used implicit mapping mode is one-to-one mapping of CCE labels to ACK labels.
In the 3GPP system, the number of symbols n occupied by the PDCCH as indicated by a physical control format indicator channel (PCFICH) in each downlink sub-frame may be 1, 2, or 3; and as for the special sub-frame, n may be 1 or 2. The value of n for each sub-frame dynamically varies. In a downlink sub-frame, under the given system parameters such as system bandwidth and pilot antenna configuration remain constant, the greater the number n of symbols occupied by the PDCCH is, the more CCEs will exist in the downlink sub-frame. When n is 1, 2, and 3, the number of CCEs in the downlink sub-frame is represented by NCCE,1, NCCE,2, and NCCE,3, and NCCE,1<NCCE,2<NCCE,3.
According to the prior art, when it requires feeding back ACKs/NACKs of N downlink sub-frames in one uplink sub-frame, the network side assigns ACK channels to the user according to the following rule.
(1) Considering that n may be provided with different values, the network side reserves f(NCCE,3) ACK channels for each downlink sub-frame (including the special sub-frame) according to the maximum CCE number, and adopts a manner of one-to-one mapping of CCEs to ACKs, in which f(NCCE,3)=NCCE,3. The function f represents a mapping rule between CCE labels and ACK channel labels. For N sub-frames, a total number of N×NCCE,3 ACK channels are reserved.
(2) The N×NCCE,3 ACK channels are divided into N consecutive portions, and each downlink sub-frame is mapped to one portion according to the original sequence, and each portion has a size of NCCE,3. For example, when it requires feeding back ACKs/NACKs of two downlink sub-frames in one uplink sub-frame, a corresponding mapping mode is as shown in FIG. 2, in which the maximum PCFICH values of downlink sub-frames 0 and 1 are both 3.
Difficulties can be experienced when implementing the foregoing rule to assign ACK channels, as unused ACK channels cannot be effectively released to form resource blocks (RBs) for the physical uplink shared channel (PUSCH) transmission.